Process for pyrolysis of coal

ABSTRACT

A process for pyrolyzing a coal feed is described. The coal feed is pyrolyzed into a coal tar stream and a coke stream in a pyrolysis zone. The coal tar stream is fractionated into at least a pitch stream. The pitch stream is hydrogenated, and the hydrogenated pitch stream is recycled into the pyrolysis zone. The hydrocarbon stream may be processed further by at least one of hydrotreating, hydrocracking, fluid catalytic cracking, alkylation, and transalkylation.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 61/906,010, filed on Nov. 19, 2013, the entirety of which is incorporated by reference.

BACKGROUND OF THE INVENTION

Many different types of chemicals are produced from the processing of petroleum. However, petroleum is becoming more expensive because of increased demand in recent decades.

Therefore, attempts have been made to provide alternative sources for the starting materials for manufacturing chemicals. Attention is now being focused on producing liquid hydrocarbons from solid carbonaceous materials, such as coal, which is available in large quantities in countries such as the United States and China.

Pyrolysis of coal produces coke and coal tar. The coke-making or “coking” process consists of heating the material in closed vessels in the absence of oxygen to very high temperatures. Coke is a porous but hard residue that is mostly carbon and inorganic ash, which can be used in making steel.

Coal tar is the volatile material that is driven off during heating, and it comprises a mixture of a number of hydrocarbon compounds. It can be separated to yield a variety of organic compounds, such as benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. These organic compounds can be used to make numerous products, for example, dyes, drugs, explosives, flavorings, perfumes, preservatives, synthetic resins, and paints and stains.

While lighter hydrocarbon streams from coal tar can be more easily processed to produce desirable products, the pitch stream includes aromatic cores that make the pitch more difficult to react in further processing. The residual pitch left from the separation conventionally is used for paving, roofing, waterproofing, and insulation.

There is a need for improved processes for making value-added products from coal tar.

SUMMARY OF THE INVENTION

One aspect of the invention involves a process for pyrolyzing a coal feed. The coal feed is pyrolyzed into a coal tar stream and a coke stream in a pyrolysis zone. The coal tar stream is separated into at least a pitch stream. The pitch stream is hydrogenated, and the hydrogenated pitch stream is recycled into the pyrolysis zone.

Another aspect of the invention includes a process for removing at least one product from coal tar. A coal feed is introduced into a pyrolysis zone, and the coal feed is pyrolyzed in the pyrolysis zone to produce a coal tar stream and a coke stream. The coal tar stream is separated into at least one hydrocarbon stream and a pitch stream. The pitch stream is hydrogenated, and the hydrogenated pitch stream is recycled to the pyrolysis zone. The hydrogenated pitch stream is pyrolyzed. At least one product is recovered from the hydrocarbon stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is an illustration of one embodiment of the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The Figure shows one embodiment of a coal conversion process 5 of the present invention. A coal feed 10 is sent to a pyrolysis zone 15. In some processes, all or a portion of the coal feed 10 is also sent to a gasification zone (not shown), where the coal feed is mixed with oxygen and steam and reacted under heat and pressure to form syngas, which is a mixture of carbon monoxide and hydrogen. The syngas can be further processed using the Fischer-Tropsch reaction to produce gasoline or using the water-gas shift reaction to produce more hydrogen. The coal feed 10 can be sent to the pyrolysis zone 15, the gasification zone, or the coal feed 10 can be split into two parts and sent to both.

In the pyrolysis zone 15, the coal feed 10 is heated at high temperature, e.g., up to about 2,000° C. (3,600° F.), in the absence of oxygen to drive off the volatile components. Pyrolysis produces a coke stream 25 and a coal tar stream 20. The coke stream 25 can be used in other processes, such as the manufacture of steel.

The coal tar stream 20 is sent to a separation zone 30 where it is separated at least a pitch stream. Preferably, the coal tar stream 20 is separated into two or more fractions 35, 40, 45, 50, 55. Suitable separation processes include, but are not limited to fractionation, solvent extraction, and adsorption. Coal tar comprises a complex mixture of heterocyclic aromatic compounds and their derivatives with a wide range of boiling points. The number of fractions and the components in the various fractions can be varied as is well known in the art. A typical separation process involves separating the coal tar stream 20 into four to six streams. For example, there can be a fraction 35 comprising NH₃, CO, and light hydrocarbons, a light oil fraction 40 with boiling points between 0° C. and 180° C., a middle oil fraction 45 with boiling points between 180° C. to 230° C., a heavy oil fraction 50 with boiling points between 230 to 270° C., an anthracene oil fraction (not shown) with boiling points between 270° C. to 350° C., and a pitch stream 55.

The light oil fraction 40 contains compounds such as benzenes, toluenes, xylenes, naphtha, coumarone-indene, dicyclopentadiene, pyridine, and picolines. The middle oil fraction 45 contains compounds such as phenols, cresols and cresylic acids, xylenols, naphthalene, high boiling tar acids, and high boiling tar bases. The heavy oil fraction 50 contains creosotes. The anthracene oil fraction (not shown) contains anthracene. The pitch stream 55 is the residue of the coal tar distillation containing primarily aromatic hydrocarbons and heterocyclic compounds.

The pitch stream 55 includes polynuclear aromatic (PNA) cores that are difficult to react for further processing, as compared to lighter hydrocarbon fractions. In the process 5, the pitch stream 55 is sent to a hydrogenation zone 60 for hydrogenating the pitch stream 55.

Hydrogenation involves the addition of hydrogen to hydrogenatable hydrocarbon compounds. Alternatively hydrogen can be provided in a hydrogen-containing compound with ready available hydrogen, such as tetralin, alcohols, hydrogenated naphthalenes, and others via a transfer hydrogenation process. The hydrogenatable hydrocarbon compounds are introduced into the hydrogenation zone 60 and contacted with a hydrogen-rich gaseous phase and a hydrogenation catalyst in order to hydrogenate at least a portion of the hydrogenatable hydrocarbon compounds. The hydrogenation zone 60 may contain a fixed, ebulated or fluidized catalyst bed.

An example hydrogenation process in the hydrogenation zone 60 takes place at a temperature between about 250° C. and about 500° C., and at a pressure between about 1.72 MPa (about 250 psig) and about 20.7 MPa (about 3,000 psig). The hydrogenation includes contacting the pitch stream 55 with a hydrogenation catalyst consisting of metal selected from the group consisting of Group VI metals (Cr, Mo, W), Group VII metals (Mn, Tc, Re) or Group VIII metals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) metals and combinations thereof supported on an inorganic oxide, carbide or sulfide support, including Al₂O₃, SiO₂, SiO₂—Al₂O₃, zeolites, non-zeolitic molecular sieves, ZrO₂, TiO₂, ZnO, and SiC. The liquid hourly space velocity (LHSV) is typically in the range from about 0.2 hr⁻¹ to about 10 hr⁻¹ and hydrogen circulation rates from about 200 standard cubic feet per barrel (SCFB) (35.6 m³/m³) to about 10,000 SCFB (1,778 m³/m³).

The hydrogenation zone 60 hydrogenates at least a portion of the aromatic cores in the pitch stream 55 to make them more reactive; for instance, the hydrogenated aromatic cores can crack open more easily in a subsequent thermal reaction. The hydrogenated pitch stream 65 with hydrogenated aromatic cores is recycled to the pyrolysis zone 15. Additional coal feed 10 can also be fed to the pyrolysis zone 15. For example, the hydrogenated pitch stream 65 can be combined with the new coal feed 10, and this combined feed can be fed to the pyrolysis zone 15, or the hydrogenated pitch stream 65 and new coal feed 10 can separately be delivered to the pyrolysis zone 15.

Pyrolyzing the recycled hydrogenated pitch stream 65, alone or with additional coal feed 10, provides a coal tar stream 20 output having lighter fractions. The pyrolysis zone 15, the fractionation zone 30, and the hydrogenation zone 60, with new coal feed 10 for pyrolysis, can provide a cycle that is repeated multiple times to provide an increased amount of the lighter fractions for additional processing.

One or more of the fractions 35, 40, 45, 50, 55 (hydrocarbon streams) can be recovered as at least one product, or may be further processed as desired to recover at least one product. In the example process 5, fraction 45 is sent to a hydrocarbon conversion zone 80. Where hydrocarbon conversion zone 80 includes a catalyst which is sensitive to sulfur, the fraction 35, 40, 45, 50, 55 can be sent to a hydrotreating zone 70 for treating to remove contaminants sulfur and nitrogen. The hydrotreating effluent 75 is then sent to the hydrocarbon conversion zone 80 for hydrocracking, for example, to recover at least one product 85.

Hydrotreating is a process in which hydrogen gas is contacted with a hydrocarbon stream in the presence of suitable catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen, and metals from the hydrocarbon feedstock. In hydrotreating, hydrocarbons with double and triple bonds may be saturated. Aromatics may also be saturated. Typical hydrotreating reaction conditions include a temperature of about 290° C. (550° F.) to about 455° C. (850° F.), a pressure of about 3.4 MPa (500 psig) to about 26.7 MPa (4,000 psig), a liquid hourly space velocity of about 0.5 hr−1 to about 4 hr−1, and a hydrogen rate of about 168 to about 1,011 Nm3/m3 oil (1,000-6,000 scf/bbl). Typical hydrotreating catalysts include at least one Group VIII metal, preferably iron, cobalt and nickel, and at least one Group VI metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. Other typical hydrotreating catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from palladium and platinum.

Suitable hydrocarbon conversion zones include, but are not limited to, hydrotreating zones, hydrocracking zones, fluid catalytic cracking zones, alkylation zones, transalkylation zones, oxidation zones, and hydrogenation zones. Example hydrotreating processes are described above.

Hydrocracking is a process in which hydrocarbons crack in the presence of hydrogen to lower molecular weight hydrocarbons. Typical hydrocracking conditions may include a temperature of about 290° C. (550° F.) to about 468° C. (875° F.), a pressure of about 3.5 MPa (500 psig) to about 20.7 MPa (3,000 psig), a liquid hourly space velocity (LHSV) of about 1.0 to less than about 2.5 hr−1, and a hydrogen rate of about 421 to about 2,527 Nm3/m3 oil (2,500-15,000 scf/bbl). Typical hydrocracking catalysts include amorphous silica-alumina bases or low-level zeolite bases combined with one or more Group VIII or Group VIB metal hydrogenating components, or a crystalline zeolite cracking base upon which is deposited a Group VIII metal hydrogenating component. Additional hydrogenating components may be selected from Group VIB for incorporation with the zeolite base.

Fluid catalytic cracking (FCC) is a catalytic hydrocarbon conversion process accomplished by contacting heavier hydrocarbons in a fluidized reaction zone with a catalytic particulate material. The reaction in catalytic cracking is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. The process typically employs a powdered catalyst having the particles suspended in a rising flow of feed hydrocarbons to form a fluidized bed. In representative processes, cracking takes place in a riser, which is a vertical or upward sloped pipe. Typically, a pre-heated feed is sprayed into the base of the riser via feed nozzles where it contacts hot fluidized catalyst and is vaporized on contact with the catalyst, and the cracking occurs converting the high molecular weight oil into lighter components including liquefied petroleum gas (LPG), gasoline, and a distillate. The catalyst-feed mixture flows upward through the riser for a short period (a few seconds), and then the mixture is separated in cyclones. The hydrocarbons are directed to a fractionator for separation into LPG, gasoline, diesel, kerosene, jet fuel, and other possible fractions. While going through the riser, the cracking catalyst is deactivated because the process is accompanied by formation of coke which deposits on the catalyst particles. Contaminated catalyst is separated from the cracked hydrocarbon vapors and is further treated with steam to remove hydrocarbon remaining in the pores of the catalyst. The catalyst is then directed into a regenerator where the coke is burned off the surface of the catalyst particles, thus restoring the catalyst's activity and providing the necessary heat for the next reaction cycle. The process of cracking is endothermic. The regenerated catalyst is then used in the new cycle. Typical FCC conditions include a temperature of about 400° C. to about 800° C., a pressure of about 0 to about 688 kPag (about 0 to 100 psig), and contact times of about 0.1 seconds to about 1 hour. The conditions are determined based on the hydrocarbon feedstock being cracked, and the cracked products desired. Zeolite-based catalysts are commonly used in FCC reactors, as are composite catalysts which contain zeolites, silica-aluminas, alumina, and other binders.

Alkylation is typically used to combine light olefins, for example mixtures of alkenes such as propylene and butylene, with isobutane to produce a relatively high-octane branched-chain paraffinic hydrocarbon fuel, including isoheptane and isooctane. Similarly, an alkylation reaction can be performed using an aromatic compound such as benzene in place of the isobutane. When using benzene, the product resulting from the alkylation reaction is an alkylbenzene (e.g. toluene, xylenes, ethylbenzene, etc.). For isobutane alkylation, typically, the reactants are mixed in the presence of a strong acid catalyst, such as sulfuric acid or hydrofluoric acid. The alkylation reaction is carried out at mild temperatures, and is typically a two-phase reaction. Because the reaction is exothermic, cooling is needed. Depending on the catalyst used, normal refinery cooling water provides sufficient cooling. Alternatively, a chilled cooling medium can be provided to cool the reaction. Aromatic alkylation is generally now conducted with solid acid catalysts including zeolites or amorphous silica-aluminas.

The alkylation reaction zone is maintained at a pressure sufficient to maintain the reactants in liquid phase. For a hydrofluoric acid catalyst, a general range of operating pressures is from about 200 to about 7,100 kPa absolute. The temperature range covered by this set of conditions is from about −20° C. to about 200° C. For at least alkylation of aromatic compounds, the temperature range is about from 100° C. to 200° C. at the pressure range of about 200 to about 7100 kPa.

Transalkylation is a chemical reaction resulting in transfer of an alkyl group from one organic compound to another. Catalysts, particularly zeolite catalysts, are often used to effect the reaction. If desired, the transalkylation catalyst may be metal stabilized using a noble metal or base metal, and may contain suitable binder or matrix material such as inorganic oxides and other suitable materials. In a transalkylation process, a polyalkylaromatic hydrocarbon feed and an aromatic hydrocarbon feed are provided to a transalkylation reaction zone. The feed is usually heated to reaction temperature and then passed through a reaction zone, which may comprise one or more individual reactors. Passage of the combined feed through the reaction zone produces an effluent stream comprising unconverted feed and product monoalkylated hydrocarbons. This effluent is normally cooled and passed to a stripping column in which substantially all C5 and lighter hydrocarbons present in the effluent are concentrated into an overhead stream and removed from the process. An aromatics-rich stream is recovered as net stripper bottoms, which is referred to as the transalkylation effluent.

The transalkylation reaction can be effected in contact with a catalytic composite in any conventional or otherwise convenient manner and may comprise a batch or continuous type of operation, with a continuous operation being preferred. The transalkylation catalyst is usefully disposed as a fixed bed in a reaction zone of a vertical tubular reactor, with the alkylaromatic feed stock charged through the bed in an upflow or downflow manner. The transalkylation zone normally operates at conditions including a temperature in the range of about 130° C. to about 540° C. The transalkylation zone is typically operated at moderately elevated pressures broadly ranging from about 100 kPa to about 10 MPa absolute. The transalkylation reaction can be effected over a wide range of space velocities. That is, volume of charge per volume of catalyst per hour; weight hourly space velocity (WHSV) generally is in the range of from about 0.1 to about 30 hr⁻¹. The catalyst is typically selected to have relatively high stability at a high activity level.

Oxidation involves the oxidation of hydrocarbons to oxygen-containing compounds, such as alcohols, aldehydes, ketones, carboxylic acids and epoxides. The hydrocarbons include alkanes, alkenes, typically with carbon numbers from 2 to 15, and alkyl aromatics, Linear, branched, and cyclic alkanes and alkenes can be used. Oxygenates that are not fully oxidized to ketones or carboxylic acids can also be subjected to oxidation processes, as well as sulfur compounds that contain —S—H moieties, thiophene rings, and sulfone groups. The process is carried out by placing an oxidation catalyst in a reaction zone and contacting the feed stream which contains the desired hydrocarbons with the catalyst in the presence of oxygen. The type of reactor which can be used is any type well known in the art such as fixed-bed, moving-bed, multi-tube, CSTR, fluidized bed, etc. The feed stream can be flowed over the catalyst bed either up-flow or down-flow in the liquid, vapor, or mixed phase. In the case of a fluidized-bed, the feed stream can be flowed co-current or counter-current. In a CSTR the feed stream can be continuously added or added batch-wise. The feed stream contains the desired oxidizable species along with oxygen. Oxygen can be introduced either as pure oxygen or as air, or as liquid phase oxidants including hydrogen peroxide, organic peroxides, or peroxy-acids. The molar ratio of oxygen (O₂) to alkane can range from about 5:1 to about 1:10. In addition to oxygen and alkane or alkene, the feed stream can also contain a diluent gas selected form nitrogen, neon, argon, helium, carbon dioxide, steam or mixtures thereof. As stated, the oxygen can be added as air which could also provide a diluent. The molar ratio of diluent gas to oxygen ranges from greater than zero to about 10:1. The catalyst and feed stream are reacted at oxidation conditions which include a temperature of about 100° C. to about 600° C., a pressure of about 101 kPa to about 5,066 kPa and a gas hourly space velocity of about 100 to about 100,000 hr−1.

An additional hydrogenation process can be provided in a hydrogen-containing compound with ready available hydrogen, such as tetralin, alcohols, hydrogenated naphthalenes, and others via a transfer hydrogenation process with or without a catalyst. The hydrogenatable hydrocarbon compounds are introduced into a hydrogenation zone and contacted with a hydrogen-rich gaseous phase and a hydrogenation catalyst in order to hydrogenate at least a portion of the hydrogenatable hydrocarbon compounds. The catalytic hydrogenation zone may contain a fixed, ebulated or fluidized catalyst bed. This reaction zone is typically at a pressure from about 689 kPag (100 psig) to about 13,790 kPag (2,000 psig) with a maximum catalyst bed temperature in the range of about 177° C. (350° F.) to about 454° C. (850° F.). The liquid hourly space velocity is typically in the range from about 0.2 hr⁻¹ to about 10 hr⁻¹ and hydrogen circulation rates from about 200 standard cubic feet per barrel (SCFB) (35.6 m³/m³) to about 10,000 SCFB (1,778 m³/m³).

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims. 

What is claimed is:
 1. A process comprising: pyrolyzing a coal feed into a coal tar stream and a coke stream in a pyrolysis zone; separating the coal tar stream into at least a pitch stream; hydrogenating the pitch stream; and recycling the hydrogenated pitch stream into the pyrolysis zone.
 2. The process of claim 1 wherein hydrogenating the pitch stream comprises contacting the pitch stream with a hydrogenation catalyst consisting of metal selected from the group consisting of Group VI metals (Cr, Mo, W), Group VII metals (Mn, Tc, Re), or Group VIII metals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) and combinations thereof supported on an inorganic oxide, carbide or sulfide support, including Al₂O₃, SiO₂, SiO₂—Al₂O₃, zeolites, non-zeolitic molecular sieves, ZrO₂, TiO₂, ZnO, and SiC.
 3. The process of claim 1 wherein hydrogenating the pitch stream takes place at a temperature between about 250° C. and about 500° C.
 4. The process of claim 1 wherein the hydrogenation takes place at a pressure between about 1.72 MPa (about 250 psig) and about 20.7 MPa (about 3,000 psig).
 5. The process of claim 1 wherein separating the coal tar stream further provides a hydrocarbon stream.
 6. The process of claim 5 further comprising: recovering at least one product from the hydrocarbon stream.
 7. The process of claim 1 further comprising: feeding additional coal feed into the pyrolysis zone; and pyrolyzing the recycled pitch stream.
 8. The process of claim 6 further comprising: processing the hydrocarbon stream to produce at least one product.
 9. The process of claim 8 wherein the hydrocarbon stream is processed by at least one of hydrotreating, hydrocracking, fluid catalytic cracking, alkylation, and transalkylation.
 10. The process of claim 9 further comprising: treating at least one product to remove contaminants.
 11. A process for recovering at least one product from coal tar comprising: introducing a coal feed into a pyrolysis zone; pyrolyzing the coal feed in the pyrolysis zone to produce a coal tar stream and a coke stream; separating the coal tar stream into at least one hydrocarbon stream and a pitch stream; hydrogenating the pitch stream; recycling the hydrogenated pitch stream to the pyrolysis zone; pyrolyzing the hydrogenated pitch stream; and recovering at least one product from the hydrocarbon stream.
 12. The process of claim 11 wherein the recovering comprises: processing the hydrocarbon stream by at least one of hydrotreating, hydrocracking, fluid catalytic cracking, alkylation, and transalkylation.
 13. The process of claim 11 wherein hydrogenating the pitch stream comprises contacting the pitch stream with a hydrogenation catalyst consisting of metal selected from the group consisting of Group VI metals (Cr, Mo, W), Group VII metals (Mn, Tc, Re) or Group VIII metals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) metals and combinations thereof supported on an inorganic oxide, carbide or sulfide support, including Al₂O₃, SiO₂, SiO₂—Al₂O₃, zeolites, non-zeolitic molecular sieves, ZrO₂, TiO₂, ZnO, and SiC.
 14. The process of claim 11, wherein hydrogenating the pitch stream takes place at a temperature between about 250° C. and about 500° C.
 15. The process of claim 11, wherein hydrogenating the pitch stream takes place at a pressure between about 1.72 MPa (about 250 psig) and about 20.7 MPa (about 3,000 psig).
 16. The process of claim 11 wherein pyrolyzing the hydrogenated pitch stream further comprises pyrolyzing additional coal feed with the hydrogenated pitch stream.
 17. The process of claim 11 wherein hydrogenating the pitch stream uses hydrogen provided in a hydrogen-containing compound selected from the group consisting of tetralin, alcohols, and hydrogenated naphthalenes.
 18. The process of claim 1 wherein hydrogenating the pitch stream comprises adding hydrogen to a hydrogenation zone.
 19. The process of claim 11 wherein separating the coal tar stream provides a plurality of hydrocarbon streams and the pitch stream.
 20. The process of claim 11 wherein hydrogenating the pitch stream uses a catalyst bed selected from the group consisting of a fixed catalyst bed, an ebulated catalyst bed, and a fluidized catalyst bed. 